A copper oxide/nitrogen-doped reduced graphene oxide (CuO/N-rGO) nanocomposite is synthesized through a low-temperature aqueous process. The resultant nanocomposite is characterized by spectroscopies which show significant interaction between copper and nitrogen. Electrochemical tests show that the nanocomposite exhibits superior oxygen reduction (ORR) activity, which is significantly higher than that of both N-rGO and CuO/GO, and is close to that of commercial Pt/C. Further mechanistic study confirms that the enhancement of ORR activity is prompted by the synergistic effect of copper and nitrogen, which largely accelerates the electrochemical reduction of the peroxide reaction intermediate on N-rGO during ORR, leading to higher onset potential, larger current density and electron transfer number. Larger porosity created by CuO intercalation also helps to lift the limiting current. The CuO/N-rGO not only serves as an alternative to the expensive Pt based ORR electrocatalyst due to its low price but is also promising for other applications such as peroxide/borohydride fuel cells and H2O2 detection/elimination. The study also gives an insight into the study method and mechanism of the metal-nitrogen synergistic effect on electrochemical catalysis which may inspire development of other new cost-effective electrocatalysts.